Chair base



FIG. 1 is a top perspective view of a chair base front face according to my new design;

FIG. 2 is a top view thereof;

FIG. 3 is an front elevational view thereof;

FIG. 4 is an rear elevational view thereof;

FIG. 5 is a left side elevational view thereof; and,

FIG. 6 is a right side elevational view thereof. 

CLAIM The ornamental design for chair base, as shown and described. 